I was pretty lucky, I didn't have to buy my bridesmaids' dresses. I have 3 of them and told them I want Tiffany color for their dresses. One of them who is a regular bridesmaid (lol), she source for 3 bridesmaid dresses of the same color, just different style (I'm not particular lah), all free size and happened that her friend's wedding have similar color theme as mine so she borrowed the dresses from the other bridesmaids (who only wore once anyways).
My suggestion is to see if you can borrow bridesmaid dresses especially those maxi dresses or free size dresses in the same color range then you'll save the money and your bridesmaids don't have to stress where to buy a dress that they will have to wear again so as not to waste it.